PYTHON:Tkinter.OptionMenu Question : option menu does not execute the command function to user selection

Question

I am trying to create a python program as below. it basically reads a file with bus time table and in the Tkinter, it displays the departure list and arrival bus stops with their corresponding time.

here i am using the following code so that it will update the time for each departure or arrival stops. but when i select the stops it does not call the functions. I do not understand why.

Tkinter.OptionMenu(self.root,self.Departure,*self.BusStops,command=self.update_departure()).pack()
Tkinter.OptionMenu(self.root,self.Arrival,*self.BusStops,command=self.update_arrival()).pac

can someone throw light on it?

the same works if it do not use a class structure.

I am running on a windows xp 2002 service pack 2 with python 2.6 version import Tkinter import time

class App():
    def __init__(self):
    self.root  = Tkinter.Tk()
    self.DEBUG_ENABLE = 1

    self.timetable_file_name = "200_timetable.txt"
    self.BusStops    = list()
    self.ArrivalTime = list()
    self.update_timetable()

    self.Departure   = Tkinter.StringVar()
    self.Arrival     = Tkinter.StringVar()
    self.StartTime   = Tkinter.StringVar()
    self.EndTime     = Tkinter.StringVar()

    self.label = Tkinter.Label(text="")
    self.label.pack()
    self.update_clock()

    self.Departure.set(self.BusStops[0])
    self.Arrival.set(self.BusStops[-1])
    self.StartTime.set("hi")
    self.EndTime.set("ih")

    self.OptMenuDep= Tkinter.OptionMenu(self.root,self.Departure,*self.BusStops,command=self.update_departure()).pack()
    self.OptMenuArr= Tkinter.OptionMenu(self.root,self.Arrival,*self.BusStops,command=self.update_arrival()).pack()
    self.OptMenuDepTime = Tkinter.OptionMenu(self.root,self.StartTime,"").pack()
    self.OptMenuArrTime = Tkinter.OptionMenu(self.root,self.EndTime,"").pack()

    self.root.mainloop()

    def debug(self,message):
    if self.DEBUG_ENABLE:
       print "DEBUG MESSAGE : ", message

    def update_clock(self):
    now = time.strftime("%H:%M:%S")
    self.label.configure(text=now)
    self.root.after(200, self.update_clock)

    def update_timetable(self):
    self.file_desc = open(self.timetable_file_name)
    for line in self.file_desc.readlines():
        self.BusStops.append(line.split('\t')[0])
        self.ArrivalTime.append(line.split('\t')[2:-1])
    self.file_desc.close()

    def update_departure(self):
    self.debug("entering update departure")
    stop_name = self.Departure.get()
    count = 0
    for stop in self.BusStops:
        if (stop == stop_name):
           break
        else:
           count += 1
    self.StartTime.set(self.ArrivalTime[count])
    count = 0

    def update_arrival(self):
    self.debug("entering update arrival")
    stop_name = self.Arrival.get()
    count = 0
    for stop in self.BusStops:
        if (stop == stop_name):
           break
        else:
           count += 1
    self.EndTime.set(self.ArrivalTime[count])
    count = 0

# The Main Program Starts Here

app=App()

""""""""""""""""""""""""" the data format is as below for file 200_timetable.txt

NICE - Station J.C. Bermond 07:30 07:45 08:00 08:10 08:15 08:30

NICE - J. Médecin / Hôtel des Postes 07:32 07:47 08:02 08:12 08:17 08:32

NICE - Grimaldi 07:33 07:48 08:03 08:13 08:18 08:33

NICE - Rivoli 07:34 07:49 08:04 08:14 08:19 08:34

""""""""""""""""""""""""""""

Answer 1

When you write command=self.update_departure() you are saying "execute the command self._update_departure, and use the result of that call as the name of the command". Since self._update_departure() returns None, it's the same as doing command=None

In other words, omit the () -- you need to pass a reference to the function.